Internet Protocol (IP) multicasting is useful for disseminating data to a large group of receivers in a network. Multicast is a form of network communication in which a transmitting node, or sender, sends a single message to multiple destinations at once. The multiple destinations are the recipients, or receivers of the message. Other methods of network communication include broadcast, in which a sender transmits to all possible recipients, and unicast, in which the sender transmits only to one specific recipient. Multicast is described in more detail in D. Comer, Internetworking with TCP/IP, Prentice Hall, 1991, Chapter 17, which is herein incorporated by reference to the extent that it is not inconsistent with the present invention.
A multicast sender node sends a message to a multicast address. The sender transmits the message to any receivers that are listening for messages at the same multicast address. A set of receivers listening for messages at a particular multicast address are associated with the sender and form a multicast group in which the receivers are group members.
As the number of receivers joining a multicast group becomes large, the sender becomes overworked and slows down as a result of having to process notifications of receipt and requests for multicast repair from group members (receivers). Multicast repair is the process of the sender resending a multicast message in response to a request for retransmission (a "repair" request) from a receiver. The increased network traffic may cause a loss of data messages due to errors and overloading in the networking equipment.